1. Field of the Invention
The present invention relates to electrical interconnection (contact) elements and, more particularly, to contact elements which are resilient contact elements suitable for effecting readily demountable pressure connections between substrates, such as electronic components.
2. Description of Related Art
Readily demountable interconnections between electronic components include resilient spring elements of one electronic component being received by another electronic component at, for example, non-resilient contact elements such as pads or sockets. The spring elements exert a contact force (optionally, with a wiping action) on the contact elements in an amount sufficient to ensure a reliable electrical connection. Resilient spring elements or structures intended to make pressure contact with an electronic component, or other substrate, are referred to herein as “spring contacts.” Both resilient and non-resilient elements or structures intended to make pressure contact with an electronic component or other substrate are generally referred to herein as “contact elements” and “contact structures,” respectively. Elements that are sized for direct demountable connection to semiconductor devices, such as semiconductor dice or wafers, are referred to as “microelectronic” contact elements, contact structures, springs, spring contacts, spring elements, or spring structures.
Prior art techniques for making spring elements generally involve stamping or etching a sheet of spring material, such as phosphor bronze, beryllium copper, steel or a nickel-iron-cobalt (e.g., kovar) alloy, to form individual spring elements, shaping the spring elements to have a spring shape, optionally plating the spring elements with a good contact material (e.g., a noble metal such as gold, which will exhibit low contact resistance when contacting a like material), and forming a plurality of such shaped, plated spring elements into an array pattern. However, such techniques are not well suited for meeting the design requirements described below.
Stringent design requirements apply to microelectronic spring contacts. Generally, a certain minimum contact force is desired to achieve reliable electrical contact to electronic components. For example, a contact force of approximately 15 grams (including as little as 2 grams or less and as much as 150 grams or more, per contact) may be desired to ensure that a reliable electrical connection is made to a terminal of an electronic component. Such terminals are often contaminated with organic films, corrosion, or oxides on their contact surfaces, and the tip of the spring contact must be applied with sufficient force to penetrate this barrier of contamination. Additionally, it is preferable for the tip of a spring contact to move in an “x” direction (i.e., parallel to the surface of the connecting terminal) when it is depressed in a “z” direction (i.e., perpendicular to the terminal surface), thereby providing “wipe,” which is useful for clearing contamination and ensuring a good connection. The tip should be disposed sufficiently above the substrate to which it is attached (i.e., the spring should have adequate “z-extension”) to ensure that an electrical connection can be made without interfering with components, such as capacitors, which may be mounted to a surface of the components to be connected.
For any spring contact, the modulus of elasticity of the spring material in combination with the shape and size of the resilient working portion of the spring should be such that the spring contact reliably provides the minimum contact force needed to ensure debris removal and an electrical connection. Application and manufacturing considerations also constrain spring shape and size. When spring contacts are fabricated at ever-smaller microelectronic scales, it becomes increasingly difficult to fulfill these, and other, design requirements. For example, certain lithographic type contact structures typically include a beam with its smallest dimension (thickness) not greater than about 50 microns, and more typically about 0.04 to 20 microns. Of course, lithographic type contact structures can be fabricated at larger scales for some applications.
Various microelectronic spring contact structures have been developed for addressing the foregoing design requirements. There is room, nonetheless, for an improved spring structure, and particularly a cantilever-type structure with a relatively large z-extension, that is readily manufactured at a very fine pitch. Additionally, there is a need for a substantially non-resilient contact structure that similarly has a relatively large z-extension and is readily manufactured at a very fine pitch.